1. Field of the Invention
The present invention relates to an active pixel sensor (APS) and in particular, to an active pixel sensor (APS) with an electronic shutter.
2. Background of the Related Art
Generally, an active pixel sensor (APS) is formed of two-dimensional sensor arrangements by which an address designation is made. As shown in FIG. 1, a related art APS includes a photo-diode D1 connected with a ground circuit and that generates a photo-electric charge based on an externally transmitted light. An NMOS transistor M1 has a drain connected with the photo-diode D1, a source that receives a power voltage Vdd, and a gate that receives a reset signal RESET. The NMOS transistor M1 is for discharging an internal electric charge of the photo-diode D1 in accordance with the reset signal RESET. An NMOS transistor M2 has a gate connected with the drain of the NMOS transistor M1 that receives a photo-electric charge from the photo-diode D1. The NMOS transistor M2 has a source that receives a power voltage Vdd to amplify the electric charges from the photo-diode D1. An NMOS transistor M3 has a source connected with the drain of the NMOS transistor M2 and a gate that receives an externally inputted row selection signal for outputting a pixel data in accordance with the row selection signal.
The reset signal RESET is inputted from an external signal source into all pixels, respectively, in order to discharge an electric charge from the photo-cell (e.g., photodiode). The row selection signals are sequentially inputted from an externally connected row decoder. In this fashion, each pixel is selected.
The operation of the related art APS will now be explained with reference to FIG. 1. When a high level reset signal RESET is inputted into the gate of the first NMOS transistor M1, the first NMOS transistor M1 is turned on. The internal electric charge of the photo-diode D1, which is generated in accordance with an externally transmitted light, is discharged and the first NMOS transistor M1 is turned off.
Thereafter, the photo-diode D1 receives externally transmitted light for a predetermined photosensitive time and generates a photo electric charge. In addition, the photo-electric charge (i.e., image signal) generated by the photo-diode D1 for a predetermined photo-electric charge time (i.e., the photosensitive time) is applied to the gate of the second NMOS transistor M2. The second NMOS transistor M2 amplifies the photo-electric charge (i.e., image signal) and outputs the amplified photo-electric charge to the third NMOS transistor M3.
The third NMOS transistor M3 externally outputs the photo-electric charge (image signal), which was amplified by the second NMOS transistor M2, in accordance with a high level row selection signal applied to its gate. Then, the high level reset signal RESET is applied to the gate of the first NMOS transistor M1, and the output signal from the first NMOS transistor M1 discharges the photo-electric charge generated by the photo-diode D1, so that each pixel returns to an initial state.
The above-described operations are repeated in the related art APS to externally output a photo-electric charge (image signal) as a pixel data. In the related art APS, when the column lines (not shown) of the pixels are selected by an external column decoder (not shown), and a photo-electric charge (image signal) is outputted to an externally connected display apparatus (television or monitor) as data of the pixels.
In the related art APS, a photosensitive time can be determined by generating a reset signal before a row selection signal is applied by controlling the period of the reset signal. In view of the photosensitive time with respect to all pixels however, the related art control method has various problems. In related art, a desired photosensitive time is obtained with respect to only a predetermined pixel. Therefore, since in the APS the pixel data are continuously read and outputted, the other pixels have different photosensitive times. Accordingly, a uniform screen brightness of a display apparatus for the related art APS is difficult or impossible to achieve.
An object of the present invention to provide an active pixel sensor (APS) with an electronic shutter that substantially overcomes at least one of the aforementioned problems or disadvantages encountered in the related art.
Another object of the present invention to provide an APS with an electronic shutter that performs an auto exposure function so that pixels have substantially equal photosensitive times.
Another object of the present invention is to provide an APS that controls a photoelectric charge, which is generated based on light transmitted to a photo-diode.
Another object of the present invention is to provide an APS that has an electric shutter performing an electronic shutter function and an auto exposure function.
Another object of the present invention is to provide an APS that enables a uniform screen brightness of a display apparatus.
To achieve at least the above objects in a whole or in parts, there is provided an active pixel sensor with an electronic sensor according to the present invention that includes a switching unit that passes through a photo-electric charge for a prescribed time in accordance with an externally inputted shutter control signal, and an electric charge storing service that stores the photo-electric charge from the switching unit and outputs the stored photo-electric charge to an output device in accordance with an externally inputted electric charge resetting signal, whereby all pixels have substantially identical photosensitive times.
To further achieve at least the above objects in a whole or in parts, there is provided an active pixel sensor with an electronic sensor according to the present invention that includes a fourth transistor having a source coupled with a drain of a first transistor and coupled to an output of a photo-diode, and a gate that receives a shutter control signal, wherein the fourth transistor is switched in accordance with the shutter control signal, and a fifth transistor having a drain respectively coupled to a drain of the fourth transistor and a gate of a second transistor, a source coupled to a ground, and a gate that receives an electric charge resetting signal, wherein the fifth transistor stores an electric charge outputted from the photo-diode through the fourth transistor and outputs the stored electric charge to the gate of the second transistor.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.